Four studies were conducted to evaluate the impact of multi-carbohydrases (MC, Rovabio® Advance T-Flex) on energy partitioning, nitrogen (N) balance and performance in broilers fed isoenergetic diets. Prior to these studies, a preliminary study was undertaken with the primary objective to evaluate bird response to dietary crude protein (CP) content (low CP [LCP] or high CP [HCP]) on energy partitioning, N balance and bird performance. The results showed that birds reared on the isoenergetic LCP diet had comparatively higher N efficiency (Nr/N intake [Ni]), as they consumed, and thus excreted, less dietary N. The LCP fed birds also presented comparatively higher energy (AME and NE) intake/N retained (Nr), and a higher ratio of energy retained as fat to total energy retained (REf/RE). As a result, these birds had a comparatively higher feed conversion ratio (FCR) and abdominal fat pad weight. This study showed that increased FCR and body fat content observed in the LCP-fed birds was due to a higher energy intake/Nr ratio.
In the first study, MC was supplemented in isoenergetic diets with either standard CP (SCP) or LCP level. Results showed that MC application increased feed energy concentration, regardless of dietary CP content. However, this resulted in energy exceeding bird requirements, and birds responded by reducing FI to control energy intake. This resulted in a decreased Ni, but, as Nr was not affected, the energy intake per Nr and WG were not impacted. Consequently, FCR was still reduced in all treatments as a result of MC application. Birds fed the LCP diet were unable to control energy intake due to the reduced dietary N content. As a result, they consumed excess energy:Nr, which increased both fat synthesis and the expression of energy related genes in the muscles (ATP5A1W, PGC-1A, COX III and ND2), regardless of MC application. The outputs from this study suggest that broilers adjust FI in response to the energy content in diets.
In the second study, MC was supplemented into diets containing two levels of soluble non-starch polysaccharides (NSP) to total NSP ratio (sNSP/tNSP), either Low (LS) or High (HS). The results showed that MC increased feed energy, regardless of the dietary sNSP/tNSP ratio. The enzymes also increased energy intake/Nr and REf/RE ratios in the HS fed birds, and N efficiency in the LS fed broilers. Accordingly, the HS fed birds exhibited excessive energy intake per Nr, thereby increasing body fat deposition.
In the third study, MC was applied in diets containing either a low (LS), intermediate (IS) or high (HS) soluble arabinoxylan (AX) to total AX ratio (sAX/tAX). This study indicated that MC reduced digesta viscosity in the HS fed birds, and increased NE content of both the HS and LS diets. MC application reduced FCR in birds fed the LS diet, and had no impact on AME/CP and REf/RE. Conversely, application of MC in the HS and IS diets did not improve FCR, because the energy released by the enzymes heightened energy intake/Nr, resulting in increased fat synthesis. In the presence of MC, birds fed the IS diet presented greater upregulation of COX III and ND2 genes in the duodenum compared to birds fed the LS and HS diet, respectively, suggesting that MC increases fat digestibility. Data from this study demonstrated that MC can increase energy utilisation in birds fed isoenergetic and isonitrogenous diets, but the likelihood of this resulting in improved WG is dictated by its impact on the energy intake:Nr ratio.
The final experiment applied MC in diets with or without probiotic (Alterion NE50, with 2.108 CFU/g of Bacillus subtilis DSMZ 29784). The results showed that MC reduced FI, irrespective of probiotic treatment, and that the probiotic increased maintenance energy (energy intake/WG), regardless of MC addition. The combination of MC with probiotic reduced WG and increased FCR. This was a result of increased maintenance requirements, possibly because the probiotic stimulated immunity, and because MC reduced FI.
Overall, data from these four studies demonstrate the ability of MC to improve feed energy levels in broiler diets. However, it must be noted that MC application in isoenergetic diets had a negative impact on FI, because the energy released by the enzymes increased energy intake per unit of N retention, thereby enhancing body fat accretion. Consequently, it is recommended that MC enzymes are supplemented to diets with inadequate energy level, ensuring that the energy released is utilised and has a beneficial effect on bird growth.